1. Field of the Invention
The present invention relates to a method and to an installation for producing energy by means of a gas turbine associated with an air separation unit.
2. Related Art
In a conventional way, a gas turbine comprises a compressor, a combustion chamber, and an expansion turbine, coupled to the compressor to drive the latter. This combustion chamber receives a combustion gas, together with a certain amount of nitrogen whose purpose is to lower the flame temperature in this combustion chamber to make it possible to minimize the emissions of nitrogen oxides to the atmosphere.
In a known way, the combustion gas can be obtained by gasification, namely by oxidation of carbon-containing products, such as coal or alternatively residues from the petroleum industry. This oxidation is performed in an independent unit known as a gasifier.
In a conventional way, it is possible to associate this gas turbine with an air separation unit. The latter, which is usually a cryogenic unit comprising at least one distillation column, is able to supply, from air, at least one gaseous stream consisting predominantly of one of the gases in the air, particularly oxygen or nitrogen.
Combining this air separation unit with the gas turbine consists in making good use of at least one of the two aforesaid gaseous streams. For this, the oxygen and nitrogen produced in the air separation unit are admitted into the gasifier and into the combustion chamber respectively.
U.S. Pat. No. 5,501,078 and EP-A-0 773 416 describe methods in which the pressures of the gases compressed by the oxygen and nitrogen compressors are constant.
U.S. Pat. No. 5,802,875 has no means for acting directly on the nitrogen compressor but a valve downstream thereof which acts indirectly on the compressor to alter the nitrogen flow rate.